Meperidine and normeperidine will be studied as stimuli for operant responding in rats and pigeons, and the nature of these drug-discrimination effects will be analyzed by testing for antagonism by narcotic antagonists, and for generalization with other phenylpiperidine analgesics. Various phenylpiperidine derivatives will also be compared after chronic administration in terms of their ability to produce naloxone-precipitated withdrawal signs. The lack of morphine- or methadone-induced cross tolerance to meperidine, anileridine, and alphaprodine found in the pigeon will be studied in the rat in order to extend the species generality of findings. The lack of antagonism of meperidine, antileridine and alphaprodine by naloxone will be extended to squirrel monkeys where previous observations suggest a difference not found in rats and pigeons. Attenuation of the non-narcotic effects of phenylpiperidine narcotics, as exemplified by the effects of normeperidine, will be attempted by pretreating animals with drugs expected to reduce the central nervous system stimulation. The drug which has been found most effective so far is pentobarbital. Studies of the phenylpiperidine analgesics with methadone maintenance and narcotic antagonists will be conducted using measures of analgesia in order to determine if, like schedule-controlled responding, the analgesia produced by these phenylpiperidine analgesics is less affected by these manipulations than analgesia produced by morphine.